Q: Our 25-year-old Aloha rose has failed to bloom again this season. It used to be in full bloom throughout the month of June. Can you recommend any treatment to restore it to its former glory? A Forsyth
A: Very probably the world’s best-known and most-loved genus of flowering plants, roses are unfortunately also vulnerable to a wide number of pests and diseases. Many of the most destructive are fungal (examples include black spot, powdery mildew, botrytis, rose rust, honey fungus, phytophthora, rose canker and grey mould), resulting in defoliation, disfigured and/or discoloured foliage, poor flowering and sometimes even death. Unsuitable soil conditions (too consistently dry, too consistently wet, too low in humus matter and nutrients) and accidental damage as a result of herbicide drift or poor pruning technique can also severely affect the plant’s health and vigour.
Classed as a short to medium-sized climber, your “Aloha” rose is a repeat-flowering climbing variety known for its large, double, coral-pink scented blooms and is generally considered vigorous and free-flowering. Happy in full sun or light shade, it typically reaches a height of 3m-4m (10-13ft). It’s hard to say for certain what is most likely to be the cause of its obvious ill-health. But just as for humans, you can do a huge amount to boost its recovery by creating the best growing conditions.
Roses are greedy, thirsty plants that need deep, fertile, humus-rich, moist and free-draining soil to flourish. For this reason, a generous mulch of well-rotted manure and/or home-made compost around the root systems every year in late winter/early spring is essential, along with a few handfuls of a slow-release organic pelleted fertiliser. Pruning is also an important way to keep most kinds of rose plants. In the case of climbing roses, pruning should typically be carried out in December until February, along with shortening side shoots by two-thirds and the tips of main branches by between a third and a half.
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In the case of your ailing plant, I’d recommend pruning it back hard to within 15-20cm of the base early next spring, followed by a generous mulching, feeding and watering. Make sure to bag and bin any prunings along with any fallen leaves as these can act as a potential source of reinfection. This harsh pruning and generous mulching/feeding/watering will remove any dead, diseased or damaged wood and kick-start your plant into producing lots of healthy new stems from the base.
Once it’s back in active growth, regular liquid feeds using Uncle Tom’s Rose Tonic will also help. The only caveat is if it’s been attacked by a soil-based fungal disease, in which case nothing will save it. Time will tell.
